1. Field of the Invention
The present invention relates to an optical pickup which scans an optical recording disk with a light beam, detects the light beam reflected therefrom and outputs an electrical signal so as to reproduce information on the disk, and more particularly to an optical pickup in which optical e elements such as a light generating device, an objective lens and a photodetector are mounted on a holder to be driven as a single body.
2. Background
Optical pickups for scanning an optical recording disk with a light beam and detecting the reflected light beam to output an electrical signal are used for audio/video laser disk players. Further, for use as portable players and in automobiles, small, lightweight laser disk players are required. To accomplish this, the optical pickup, which occupies a relatively large space inside the player, should be lighter and smaller. A small optical pickup enables the miniaturization of the players, and as a rule is favorable for portable use and for use in automobiles. Besides being beneficial for the laser disk player, a lightweight optical pickup greatly contributes to the high speed data processing of a compact disk ROM system or magneto-optical disk drive which is used as a computer's peripheral device.
FIG. 1 illustrates a simplified conventional optical pickup. As shown in FIG. 1, the optical pickup comprises a laser diode 1 for generating a laser beam, a grating 2 for diffracting the laser beam into three beams, a half mirror for passing portions of the incident laser beams and reflecting the remainder, an objective lens 4 for focusing the laser beams on a disk 5, a cylindrical lens 6 for changing the focusing position and shape of the laser beams using astigmatism, and a photodiode 7 for sensing the laser beams reflected by disk 5 and focused by cylindrical lens 6 to detect an electrical signal such as a playback signal or focusing/tracking error signal. In order to compensate for the focusing/tracking error due to the vibration of disk 5, objective lens 4 is mounted on actuator coils 8 so as to be driven in the horizontal and vertical directions with respect to the disk. The entire optical pickup is installed so as to be conveyed in the radial direction of disk 5 by a conveyer such as a voice coil motor (not shown), to seek particular information stored on the disk 5.
Such a mechanical configuration of an optical pickup is divided into two types, a single-body type wherein an objective holder 9 is driven with an optical pickup main body 10 as a single, integral body, and a separated type wherein the objective lens holder 9 is separated from the main body 10 so as to be independently driven. The single-body type is highly desirable because of its stable operation and because few focusing/tracking servo errors occur. However, the single-body type is disadvantageous in that high-speed search operations may not be performed since the actuator coil 8 must drive the entire optical pickup.
Thus, the separated type optical pickup is usually used in computer peripheral devices such as the compact disk ROM system or magneto-optical disk drive, since the actuator load of the separated type is small. However, the critical shortcoming of the separated type is that when the objective lens is moved its optical axis deviates from that of the main body so that aberration of the objective lens becomes larger and servo errors occur frequently.
Referring to FIG. 1, the laser diode 1, objective lens 4 and photodiode 7, are typically arranged in a T-shaped configuration with the half mirror 3 being disposed at the point of intersection. Since such a large space is unnecessarily occupied, this configuration is unfavorable for miniaturizing the optical pickup. In other words, since the conventional optical pickup is generally relatively large and heavy due to its optical element configuration, miniaturization of the player (or drive) and the increase of data processing capability is difficult to achieve.